The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.
1. Field of the Invention
This invention relates to a process of post-treating anodized aluminum(s), and to the composition for treating anodized aluminum(s) to improve adhesion-bonding, abrasion-resistant, and the corrosion-resistant properties. More specifically, this invention relates to a novel composition, and to the process of using the composition to seal or post-treat anodized aluminum and anodized aluminum alloys. The trivalent chromium post-treatment (TCP) composition comprises an acidic aqueous solution containing effective amounts of at least one water-soluble trivalent chromium salt, an alkali metal hexafluorozirconate, at least one alkali metal tetrafluoroborate and/or hexafluorosilicate and effective amounts of water-soluble thickeners and/or water-soluble surfactants.
2. Description Of Prior Art
Anodized aluminum(s) are generally sealed or post-treated after anodizing by processes employing a variety of sealing compositions. Current high-performance post treatments or sealers for anodized aluminum are based on hexavalent chromium chemistry. Hexavalent chromium is highly toxic and a known carcinogen. As a result, the solutions used to deposit these protective coatings and the coating per se are toxic. These films do, however, yield outstanding paint adhesion, abrasion, and corrosion resistance to the anodized aluminum. Typically, seal coatings are deposited onto the anodized coating at elevated temperatures and are usually applied by immersion or spray processes. Post treatments are usually called out by the military or commercial specifications that govern each coating being treated. As such, there is not a unique xe2x80x9cpost treatmentxe2x80x9d specification for all anodize aluminums like there is for xe2x80x9cconversion coatingxe2x80x9d aluminums.
Further, environmental laws, executive orders, and local occupational, safety, and health (OSH) regulations are driving military and commercial users in the search for hexavalent chromate-free post treatments. In the case of anodized aluminums, the anodize film and base metal are relatively non-toxic. With the addition of the required hexavalent chromate post treatment, these coatings become toxic. Other post treatments, such as nickel acetate, and various fluoride compounds do not contain chromates, but their technical performance is inferior to the chromate-based coatings. In addition, the use of chromate post treatments is becoming more expensive as regulations tighten. Costs may become prohibitive with future restrictions imposed by the EPA. Thus, while existing chromate post treatments are outstanding in their technical performance in that they provide enhanced corrosion protection and adhesion bonding e.g. paint and other coatings at a low application cost, from a life-cycle cost, environmental, and OSH perspective, hexavalent chromate coatings are detrimental for people and the environment.
This invention relates to a novel composition and to the process of using said composition to post-treat or seal anodized aluminum and its alloys at ambient temperatures or higher e.g. ranging up to about 200xc2x0 F. More specifically, this invention relates to a composition for post-treating anodized aluminum and its alloys to improve the corrosion-resistance and adhesion bonding properties e.g. paint adhesion etc. The trivalent chromium post-treatment (TCP) composition comprises an acidic aqueous solution having a pH ranging from about 2.5 to 4.5 and preferably 3.7 to 4.0,and per liter of said solution, from about 0.01 to 22 grams of a water-soluble trivalent chromium salt, about 0.01 to 12 grams of an alkali metal hexafluorozirconate, about 0.01 to 12 grams of at least one fluoro-compound selected from the group consisting of an alkali metal tetrafluoroborate, an alkali metal hexafluorosilicate and various combinations thereof, from about 0 to 10 grams and preferably 0 to 2.0 grams of at least one water-soluble thickener, and from 0 to 10 and preferably 0 to 10 grams of at least one water-soluble non-ionic, cationic or anionic surfactant.
It is therefore an object of this invention to provide an aqueous solution comprising a trivalent chromium salt, an alkali metal hexafluorozirconate, and a tetrafluoroborate and/or hexafluorosilicate for post-treating, anodized aluminum and its alloys to improve the adhesion bonding, abrasion, and corrosion-resistance characteristics.
It is another object of this invention to provide a stable acidic aqueous solution having a pH ranging from about 2.5 to 4.5 containing a trivalent chromium salt for treating or sealing anodized aluminum and its anodized alloys.
It is a further object of this invention to provide a stable acidic aqueous solution having a pH ranging from about 3.7 to 4.0 containing trivalent chromium for treating or sealing anodized aluminum and its alloys at about room temperature wherein said solution contains substantially no hexavalent chromium.
These and other objects of the invention will become apparent by reference to the detailed description when considered in conjunction with the accompanying FIGS. 1-6(photos).